Rotary drilling methods are commonly used in the drilling of oil and gas wells. Typically, the wellbore which extends from the surface into one or more subterranean oil and/or gas producing formations is drilled by a rotary drilling rig on the surface which rotates a drill bit attached to a string of drill pipe. The drill bit includes rotatable cutting surfaces so that when the drill bit is rotated by the drill string against subterranean strata under pressure a bore hole is produced.
Typically, a drilling fluid is circulated downwardly through the drill string, through the drill bit and upwardly in the annulus between the walls of the wellbore and the drill string. The drilling fluid functions to maintain hydrostatic pressure on formations penetrated by the wellbore, which helps to prevent pressurized formation fluids from flowing into the wellbore, and to remove cuttings from the wellbore. As the drilling fluid is circulated, a filter cake of solids from the drilling fluid forms on the walls of the wellbore, which may result from initial fluid loss to the formation and may prevent additional fluid loss. The drilling fluid also cools and lubricates the drill bit.
The hydrostatic pressure created by the drilling fluid in the wellbore may fracture weak formations penetrated by the wellbore which can cause drilling fluid to be lost into the formations. When this occurs, the drilling of the wellbore must be stopped to seal the fractures, which is a time-consuming and expensive process.
Another problem with drilling and completing wellbores occurs when the wellbore is drilled into and through unconsolidated weak zones or formations (e.g., formed of clays, shales, or sandstone). The unconsolidated portions of the formation can slough off the sides of the wellbore, which enlarges the wellbore and often causes the drill bit and drill pipe to become stuck. If this occurs, drilling must be stopped and remedial steps taken.
The problems that can occur with drilling become more frequent or pronounced with infield drilling, drilling below old fields, and striving for deeper targets. Each of these situations has become more common in recent years.
A typical technique for solving these problems that can occur during drilling includes putting a casing or liner into the wellbore and sealing the wellbore with, for example, cement in the annular space between the walls of the wellbore and the exterior surface of the casing or liner. This technique of cementing pipe in the wellbore as the drilling progresses has a number of disadvantages including the time and expense incurred in placing and sealing the pipe as wellbore as the reduction in the wellbore diameter after each casing point. That is, the well diameter must be reduced below each casing point so that a smaller casing can be lowered through the previously placed casing and sealed in the wellbore.
Thus, there are needs for improved methods of drilling wellbores and strengthening unconsolidated weak zones or fractures in a geological formation.